Arisaema (Arisaema thunbergii subsp. urashima)
Arisaema thunbergii subsp. urashima, a striking Japanese cobra lily, excels in deep shade with medium to wet moisture needs.
Complete Plant Information
Overview
The striking Arisaema thunbergii subsp. urashima, commonly known as Arisaema, brings an unmistakable tropical flair to shaded garden corners. Native to woodlands in Japan, this herbaceous perennial is prized for its uniquely shaped and patterned spring flowers, which resemble a cobra’s head, leading to its nickname, the cobra lily. Gardeners seek out this Arisaema variety for its architectural presence and bold foliage display during the growing season.
This species thrives where many other ornamentals falter, preferring deep shade and consistent moisture. Arisaema thunbergii subsp. Urashima emerges early; its spathe appears before or alongside the solitary, hand-shaped leaf structure. While it holds visual interest through summer dormancy, careful site selection is crucial to ensure its preference for humus-rich, moist but well-drained soil is met, especially for successful winter survival in cooler zones.
With its dramatic flower structure and lengthy, trailing spadix, the Arisaema thunbergii subsp. urashima provides high visual impact in woodland settings. Though it requires medium maintenance and patience if grown from seed, its unique aesthetic rewards the dedicated gardener looking to capture the mystery of the Japanese forest floor.
Fast Facts
- Plant Family: Araceae
- Plant Type: Herbaceous perennial
- Native Range: Japan
- Hardiness Zones: USDA Zones 5-9
- Size at Maturity:
- Height: 1-2 ft
- Spread: 1-2 ft
- Bloom Time: April to May
- Bloom Description: Purple and white
- Sun Exposure: Part shade to full shade
- Water Needs: Medium to wet
- Maintenance Level: Medium
How to Grow
Planting the tubers of Arisaema thunbergii subsp. urashima should occur in autumn or early spring, positioning them about 3-4 inches deep. The ideal location offers protection from intense midday sun, favoring part shade to full shade conditions, mirroring its native woodland habitat. Crucially, the soil must be rich in organic matter (humus) and remain consistently moist; this plant does poorly if the location experiences heavy clay soils or periods of drying out.
Watering is a vital component of care for this Arisaema species; aim for deep, regular moisture, particularly during its active growth phase in spring. Fertilizing is generally not required if the soil is rich and amended annually with compost. Deadheading spent flowers is optional, though allowing the spathe to wither may result in a mid-summer display of attractive red berries, provided the plant sets fruit.
Note that this plant goes dormant during the summer heat, so ensure surrounding plants do not completely obscure its location during this rest period. While winter hardy to Zone 5, providing shelter in northern Zone 5 gardens, such as within the St. Louis area recommendation, is prudent. Be aware that propagation from seed is slow, often requiring 3 to 5 years before the plant matures enough to produce its signature bloom.
Landscape Uses
The cultural needs of Arisaema thunbergii subsp. urashima—deep shade and constant moisture—make it an outstanding choice for specialized areas like rain gardens, fulfilling its listed suggested use perfectly. These plants naturally form drifts, so planting them in groups of three or more enhances their visual drama as the cobra-like flowers emerge together.
They are ideally suited for established shady woodland gardens or native plant areas where they can remain undisturbed for many years, allowing the tubers to mature fully. Because they disappear entirely into summer dormancy, pair them with later-emerging, shade-tolerant groundcovers that can fill the void. Think about pairing the bold forms of Arisaema with ferns or hostas that enjoy similar moist, dark conditions.
This genus brings an exotic, architectural structure to the understory. Use Arisaema thunbergii subsp. Urashima along shaded paths where structure is needed or beneath high canopy trees where sunlight is scarce, letting their unique form take center stage in early spring.
Standout Features
Flower Qualities
- Showy
Fruit Qualities
- Showy
Noteworthy Characteristics
The Arisaema thunbergii cobra lily is a woodland perennial native to Japan, related to the American jack-in-the-pulpit. Its remarkable spring flower features a pitcher-like spathe striped purple and white, topped by a dark purple, pointed hood resembling a cobra’s head. A long, purple, whip-like tail trails up to 24 inches from the spadix emerging from the flower throat, contributing significantly to its tropical appearance. Subsp. Urashima is slightly smaller than the species and is named after the legendary Japanese fisherman, Urashima Taro.
Tolerances
- Heavy Shade
- Wet Soil
Potential Problems
This particular Arisaema exhibits very few issues regarding pests or diseases, meaning it rarely suffers from serious insect or fungal complications under optimal conditions. Proper drainage prevents the most common threat: tuber rot, which occurs if the soil becomes too waterlogged or heavy. Avoid planting in heavy clay, as this stifles air flow essential for tuber health and predisposes the plant to root issues.
Frequently Asked Questions
What hardiness zones is Arisaema suitable for?
The Arisaema thunbergii subsp. urashima is best suited for USDA Hardiness Zones 5 through 9. Be mindful if planting in Zone 5, as providing winter shelter is recommended.
How large does Arisaema grow?
This herbaceous perennial typically reaches a mature height between 1 and 2 feet tall, with a comparable spread of 1 to 2 feet wide.
When does Arisaema bloom?
The incredible bloom period for Arisaema thunbergii subsp. urashima occurs in the spring, generally from April to May, displaying unique purple and white coloration.
What sun exposure does Arisaema need?
For optimal flowering and health, this plant requires significant low light, thriving best in conditions ranging from part shade to full shade.
Conclusion
The exotic charisma of the Arisaema thunbergii subsp. urashima, marked by its distinctive cobra-like flowers and robust foliage, makes it an invaluable specimen for deep shade gardens. Its requirements for consistently moist, humus-rich soil align perfectly with creating naturalistic woodland beds. Before planting your Arisaema, confirm your site offers adequate moisture and protection from intense sun to ensure this unique Japanese native flourishes for years to come.
Companion Planting
Given the need for consistent moisture and deep shade, companion plants should share cultural requirements with Arisaema thunbergii subsp. urashima. Ferns are excellent partners; native species like the Tassel Fern (Polystichum acrostichoides) or Japanese Painted Ferns offer contrasting textures that complement the bold Arisaema leaves. Consider incorporating shade-loving groundcovers like wild ginger (Asarum species) to maintain ground moisture during the summer dormancy of the Arisaema.
Good companions also include moisture-loving perennials that emerge later in the season, such as Hosta cultivars with blue or textured foliage that won’t compete heavily in early spring. Epimediums are another excellent choice; they provide early color and then form a supportive mat that protects the soil around the overwintering tubers of the Arisaema.
Seasonal Care Calendar
Early Spring (Pre-Emergence): Lightly top-dress the area around your Arisaema with a thin layer of well-rotted compost, but avoid layering it too deeply over the dormant crown. Monitor soil moisture, ensuring it remains damp as temperatures rise prior to leaf-out.
Late Spring to Summer (Active Growth & Dormancy): This is the critical watering period when flowers and foliage are actively growing. Water deeply whenever the surface begins to approach dryness. Once the foliage begins to yellow and die back in mid-summer heat, cease supplemental watering, as the Arisaema thunbergii subsp. Urashima requires dry conditions during dormancy to prevent rot.
Autumn: Mild weather signals tuber thickening. Keep the area weed-free but avoid any deep digging or disturbing of the soil directly above the tubers. This is the best time for planting new tubers or dividing established clumps, if necessary.
